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How Best to Charge Your Phone, Explained by an Expert

How often to charge, how much to fill up, and more.

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Hunter Kelley

Welcome to Product Support, a column devoted to helping you get the most out of the gadgets and software you already use.

Keeping your gadgets charged is easy in the short term. Just keep an eye on their battery level and plug them into the wall when it gets low. But keeping your gadgets’ batteries healthy in the long run is a much more complicated proposition. The lithium-ion batteries we have in virtually all of our gadgets are chemically destined to degrade over time, holding less charge than they used to, and blowing through what little they have faster then before. It’s impossible to stop this process, but it is possible to slow it.

To find out the best ways to postpone the inevitable, we talked to Isidor Buchmann, CEO and founder of Cadex Electronics and main contributor to extremely in-depth and invaluable online resource Battery University, about how exactly you should treat your batteries in a perfect world, what you can do to maximize their life.

So brace yourself, because here’s what you’re probably doing wrong.

Is it bad to charge my phone to 100 percent?

It's not great!

It may put your mind at ease when your smartphone’s battery reads 100 percent charge, but it’s actually not ideal for the battery. “A lithium-ion battery doesn’t like to be fully charged,” Buchmann says. “And it doesn’t like to be fully charged and warm.”

In a perfect world, your battery never goes below 20 percent, and never above 80.

If you’re on a device that runs iOS 13 or higher, you’re in luck because Apple’s new Optimized Battery Charging option allows you to do exactly this. That way, you can avoid getting all the way to the top overnight and instead, just top up over the course of the day. It's not deadly for your phone to be full, of course. But it will cause it to age slightly faster so it's good to avoid if you can!

Is it bad to run your phone down to zero?

This is also not great!

Charging your battery all the way up is less than ideal, and to make matters worse, so is discharging it down to zero. While older nickel-cadmium batteries did have a “memory” that could be disrupted by anything other than a full cycle from full to empty, your modern lithium-ion battery abhors both extremes.

At what percentage should I charge my phone?

In a perfect world, your battery never goes below 20 percent, and also never above 80 percent.

Electric vehicles, with batteries that are required by various regulations to have a minimum operational life on the order of several years, make that prospect more feasible than it is for your phone by using drastically oversized batteries that are purposefully designed to never be fully charged. “You’ll typically charge to about 80 percent and discharge down to about 20,” Buchmann says. “In that mid-range use, you get far more cycles than if you fully charged and discharged as we do on our cellphones.”

Is it bad to charge your phone multiple times a day?

Nope! It's fine. Good even!

Lithium-ion batteries like to be charged in short spurts, so plugging in for five percent here and 10 percent there is not only fine, but advisable. Cycling your phone from 100 percent, down to zero, and back up has a very limited utility in that it can “recalibrate” a battery if it’s doing strange things like dying out of nowhere when it claims to be decently charged, says Buchmann. “But other than that, it’s not advised to fully cycle lithium-ion.”

What's the worst thing for my phone's battery?

To be very warm and fully charged at the same time. Avoid this!

The most stressful thing that can happen to your phone’s battery during regular use is not, in fact, being discharged, or even being empty. “The combination of full charge and warm actually causes more stress than usage,” Buchmann warns. “If you’re in a car in the summer, don’t put it on the dashboard. Put it on the floor, or in the shade.”

Circumstances where your phone or laptop are fully charged and extremely hot should be relatively rare and, as such, relatively avoidable. Don’t leave your fully-charged phone in the summer sun! Perhaps the most dangerous recurring heat-and-charge combination is a laptop that is always plugged in and prone to running hot, in which case investing in a cooling stand may be a smart move in case you ever want to use your laptop away from its tether.

Is it OK to use a wireless charger?

Yes, especially if it helps you maintain that 20 to 80 percent charge.

While lithium-ion batteries don’t like to be hot when they’re full, Buchmann says recent studies on vehicle batteries suggest they do like to be warm while they charge and discharge, so your wireless charger is probably not terrible for your battery’s health even though it may create additional heat. And if it helps you stay within the 20 to 80 percent power band, that's a very good thing.

“For charging and discharging, the battery likes to be warm. Between 25 and 40 degrees Celsius (77-104 F),” Buchmann says. “But in storage, the battery should be cool, maybe 15 or 10 degrees Celsius (59-50 F).” Monitoring these temperatures constantly is a tall order and probably not feasible, but you can find apps that will take note of your batteries temperature and warn you if it hits extremes, which will at least help you avoid the worst scenarios.

How much do I need to worry about all this?

Honestly, not that much.

It’s good to know the battery basics so you can avoid the worst pitfalls, but it’s also important to not fall into the trap of trying to be perfect. In the end, a lot of this is completely out of your hands. Despite the fact that lithium-ion batteries power a lot of our everyday life, the science of exactly how they function in practice is very much still in development, with new nuances still being uncovered. And much of the emerging science comes from tests on huge multi-cell vehicle batteries, which are similar but not identical to the single-cell battery in your phone. On top of that, your day-to-day charging usage experience is so riddled with variables that it’s pretty much impossible to confirm whether or not you’re doing things right.

But perhaps most importantly, your phone is not going to last forever, and not even super-humanly good battery treatment is going to change that. A screen replacement that’s just slightly too expensive to be worth it for your aging phone or outdated processor that can’t handle the latest software is all but destined to end your phone’s usable life even if the battery doesn’t. And until or unless the companies that make phones start designing them to survive a much, much longer lifespan, there’s not a whole lot you can do as the end user.

Just like your battery’s charge is a resource that you spend for the convenience of checking your phone, consider your battery’s overall lifespan as a resource you’ll need to spend wisely to preserve your own sanity. It’s up to you to decide what safeguards are worth the trouble.

“Why have a perfectly good battery when the glass is broken or the phone becomes obsolete?” Buchmann asks. “It all sort of harmonizes together to come to an end.” You’ll never prevent it, but armed with what you know now, maybe you’ll be able to postpone it a little bit longer.

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